In a turbine, alignment of stationary flowpath components with respect to rotating flowpath components, such as a shaft or rotor wheel, is crucial. Typically, some spacing must be provided between the stationary and rotating flowpath components. If the alignment is off, then the spacing between the stationary and rotating flowpath components may be to large or to small. If the spacing is to large, then there may be to much leakage of a motive fluid, such as steam, between the stationary and rotating flowpath components and thus a decrease in overall efficiency of the turbine. If the spacing is to small, then the stationary flowpath components may rub against the rotating flowpath components damaging the turbine.
Transient temperature differentials typically experienced by the turbine during normal operations make it difficult to properly align and space the stationary flowpath components with respect to the rotating flowpath components. When stationary flowpath components lose alignment with the rotating flowpath components the efficiency of the turbine is decreased and/or the turbine may be damaged.
One technique for supporting and centering stationary flowpath components with respect to the rotating shaft involves the use a pair of lug arrangements for the upper half of a diaphragm and another pair of lug arrangements for the lower half of the diaphragm. One example of such a system is disclosed in U.S. Pat. No. 2,247,423 to Webster which is herein incorporated by reference. With this technique, proper centering of the diaphragm requires that the diaphragm's center coincide with the center or axis of the casing which means that the face of the lower half of the diaphragm be located in a plane through the joint or dividing plane between the casing halves. Lug arrangements on opposite sides of the lower half of the diaphragm are used to achieve this and hold the diaphragm in place in the lower half of the casing. Similarly, lug arrangements on opposite sides of the upper half of the diaphragm are used to locate the face of the upper half of the diaphragm in a plane through the joint or dividing plane between the casing halves. Additionally, the lower half of the diaphragm is centered horizontally in the lower casing half by a vertical pin secured in a groove in the bottom portion of the lower casing half and slidably projecting into a vertical bore in the lower half of the diaphragm.
Unfortunately, this technique has some problems. For example, when this technique is used, proper sealing at the split line between halves of the diaphragm is difficult because the lug arrangements are concerned with centering the lower and upper halves of the diaphragm with the face at the split line for the lower and upper casing halves, respectively, and not with forming a tight seal between the diaphragm halves. Additionally, with this technique the diaphragm halves are not properly aligned because they are aligned with respect to the casing, not the shaft.